In cases like this it is difficult to know whether the problem stems from fedora 12 or from an only semi-successful upgrade. One way to find out would be to back up your personal stuff and then try a fresh install of f12. At least, you have some hard-won experience at getting it running.
I hesitate to suggest that you give up a functioning system, when it's possible you might have to repeat all your work to get f12 running. Maybe a wiser course would be to wait a while and see if updates improve your system, or if the problems get worse.